Place puff pastry sheet on a baking paper lined baking tray. Score a 2 cm border around the pastry. Lightly score the pastry except the border. Chill in the fridge until ready for use.
Chocolate pecan paste: place all the ingredients into a food processor and blend until it forms a thick paste.
Cut the pears in quarters and remove the seeds. Slice each wedge into thin uniform slices. Discard (or eat) the odd or small ones. Place sliced pears in a bowl and lightly toss together with the lemon juice, corn flour, vanilla and castor sugar.
Preheat the oven to 220°C.
Spread the chocolate paste within the borders of the chilled pastry.
Arrange the pears overlapping one another on top of the chocolate paste.
Brush the pears with melted butter and sprinkle with treacle sugar.
Bake for 10 minutes then turn heat down to 180°C and bake for a further 10 – 15 minutes or until golden brown. Allow to cool for a few minutes.
Slice into portions, dust with a little icing sugar and serve with a good dollop of crème fraiche or mascarpone.
Optional: Dust the pears generously with icing sugar and use a blow torch for extra caramelization.